Mechanisms of dyspnoea relief and improved exercise endurance after furosemide inhalation in COPD

¹ Queen's University, Canada

^* To whom correspondence should be addressed. E-mail: odonnell{at}queensu.ca.

Accepted 16 January 2008

	Abstract

Objectives:This study examined the effects of inhaled furosemide on the ventilatory and perceptual response to high intensity, constant-load cycle exercise in chronic obstructive pulmonary disease (COPD).

Methods: In a randomized, double-blind, placebo-controlled, cross-over study, 20 patients with COPD (forced expiratory volume in 1 sec 45 ± 15 % predicted; mean ± SD) received either nebulized furosemide 40 mg or placebo on two separate days. Thirty minutes after each treatment, patients performed pulmonary function tests and a symptom-limited cycle exercise test at 75% of their maximum incremental work-rate. Post-dose changes in spirometry, plethysmographic lung volumes, dynamic operating lung volumes, ventilation, breathing pattern, cardiovascular function, dyspnoea intensity and exercise endurance time were compared between-treatments.

Results: After treatment with furosemide compared with placebo, dyspnoea intensity at the highest equivalent exercise time (i.e., isotime for each patient) decreased by 0.9 ± 1.0 Borg units (p<0.01), with attendant improvement in exercise endurance time by 1.65 ± 0.63 min (p<0.05). These improvements were associated with increases in dynamic inspiratory capacity, tidal volume and mean tidal expiratory flow rates at isotime (p<0.01). The eight patients who improved exercise endurance time by >1 min had greater changes in operating lung volumes (p<0.05), submaximal oxygen pulse (p<0.05) and oxygen uptake (p=0.05) compared with those who did not.

Conclusion: Our results suggest that alleviation of exertional dyspnoea after single dose furosemide inhalation in COPD is multifactorial but that improvements in dynamic ventilatory mechanics are contributory in some individuals.

Keywords: COPD, dynamic lung hyperinflation, dyspnea, exercise, furosemide